1. Field of Invention
The invention relates generally to inspecting tubulars in a subterranean wellbore. More specifically, the present invention relates to a device and method that uses a radiation source for inspecting a subterranean tubular and a radiation detector for detecting or identifying the presence of an unwelcome or egregious substance or substances deposited in and/or adjacent the tubular.
2. Description of Prior Art
Subterranean wellbores used for producing hydrocarbons typically are lined with a casing string that is cemented to the formation intersected by the wellbore. An inner casing string may also be inserted within the first casing string and cemented in place. Fluid produced from the well flows to the surface within production tubing that is inserted inside the inner casing string. Over the life of a typical well the production tubing may be removed so that remediation, repair, or flow enhancement operations may be conducted in the well. There may also be a need at some time for removal of a portion or for all of the casing.
Generally drilling fluids fill the annular space between the concentric tubulars. Particulates, such as barite, within the drilling fluids may settle out or precipitate over time and form a cement like substance that binds together the concentric tubulars and prevents the removal of the inner tubular from the wellbore. While cutting tools can sever the tubulars to enable removing the unstuck portion, the tubular cannot be removed if the cut is made at a depth below where the tubulars are adhered together. Alternatively, too shallow a cut can leave an undesirably long portion of free pipe extending above the point of adhesion. Asphaltene or sand mixed with heavy hydrocarbons can form blockages inside the production tubulars which will limit well production capability. Junk-baskets, gauge rings and dummy tools run through the production tubing have been used to look for blockages.